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Historic, archived document 

Do not assume content reflects current 
scientific knowledge, policies, or practices. 









April 13, 1953 



By J. W. Duff ie Id and F. I. Righter 

Fcrest Geneticists, California Forest and Range Experiment Station 

Pine hybrids produced up to 194 at the Institute of Forest 
Genetics were lasted in a recent publication to acquaint plant breeders 
a-<xl botanists with the progress of the hybridisation wcrl< (7)i/. 
Numerous requests for information about pine hybrids indicate that a 
different type of publication on the pine hybridisation program is 
needed; namely, a list of the hybrids by common names of their parental 
species, giving a digest of our present knowledge obtained from results 
of tests conducted at the Institute and elsewhere and our surmises 
about the regions where the hybrids may be of value. This paper is 
directed at that need. 

Most plant hybrids can be expected tc be intermediate between 
their parent species in most quantitative characters. Sometimes 
hybrids resemble one parent in a certain character, such as resistance 
to the pine reproduction weevil which the Jeffrey-Coulter pine hybrid 
inherits from Coulter pine (A) . Less frequently, a hybrid may exceed 
both parents in rate of growth or some other quantitative character. 
This phenomenon is known as hybrid vigor. Even the truly intermediate 
hybrid "may have some advantages. It may, for example, be able to 
tolerate the adverse climate tc which its slower -growing parent is 
adapted and in which its faster-growing parent cannot survive. Thus 
almost any hybrid has potential value and merits at least small-scale 
testing in the appropriate regions. 

l/ Numbers in parentheses refer to bibliography at end of 

paper . 


Agriculture — Berkeley 


Suggestions given here on geographic and climatic adaptability 
should he recognized merely as suggestions. They are often based not 
on actual trials or careful studies of comparative climatology, but 
on information about ' adaptation of pine species in various parts of 
the world gleaned from the literature and from conversations with 
visiting foresters from virtually every major coniferous forest 
region of the world. 

With regard to the availability of hybrid seed for testing or 
large scale planting by others, some explanation of the Institute's 
situation and policies is necessary. The Institute wishes to get 
comprehensive information on the economic possibilities of the hybrids 
which perform well at Placerville . This information would in the 
future enable the Institute and other breeding agencies to breed for 
specific purposes with greater precision than would otherwise be 
possible. Such information can be obtained only from tests estab- 
lished on suitable sites in various regions in the United States and 
in foreign countries by cooperators having the knowledge, facilities, 
and resources requisite for properly conducting the tests. This means 
that the objectives and methods must be clearly understood and agreed 
to in advance ; that the cooperator must have both control over the 
area Involved and the personnel and means with which to maintain the 
test and obtain the desired data on performance. As research insti- 
tutions are best qualified in those respects, the Institute favors 
them as cooperators; and accordingly most of its cooperative field 
tests are being conducted by other Forest Service experiment stations 
and by other research and educational institutions. Wood-using and 
timber -growing industries and other private parties having the 
requisite resources are welcomed as cooperators when seed is available. 
No administrative procedure has been set up to enable the Institute to 
make its products available for other than scientific purposes, except 
to the U. S. Forest Service. 

Unless otherwise stated, all tests so far made, have been con- 
ducted at the Institute of Forest Genetics at Placerville, California, 
latitude 39° north, longitude 121° west, altitude 2700 feet above sea 
level. Temperature and precipitation data are as follows: 


Temperature and Precipitation 
Institute of Forest Genetics 


:Max. temp. 
: 1929-37 

:Mean temp. 
: 1929-3 7 

:Min. temp. 
: 1929-37 

: Precipitation: Snowfall 
: 1930-3' 7 : 1928-37 









7 ?A 

i / / n 





7 DP 

1 5^ 


59 5 

> y • s 

50 1 

Z0 7 








l id,y 

71 ft 


















• 57.6 
























22. ' 7 

The outstanding features of this climate are long dry summer, mild 
rainy winter, and occasionally 20 inches or so of heavy, wet snow which 
damages certain of the introduced pines. The soil at the Institute, 
Aiken clay loam, has a rather high moisture -holding capacity, and despite 
the long summer drought, moisture is available to tree roots in the lower 
horizons. Pot culture tests have shown that the levels of available 
phosphorus a^d nitrogen in Aiken clay loam are rather low. The conifers 
growing spontaneously at the Institute are Pinus ponderosa Laws., P. 
sab in! ana Dougl., P. lambertiana Dcugl., Ps taxif olie. (P ir.) 
Britton, and Libocedrus decurrens Terr. 

In the annotated list which follows, the name of the seed-parent 
species is given first, the pollen parent second. English names are those 
given in Standardized Plant Names Q) . The year-date which follows is 
the year in which the cross was first successfully made at the Institute. 
The list is not a complete catalogue of hybrids produced at the Institute 
of Forest Genetics (hereafter abbreviated as IFG) — some hybrids unlikely 
to have practical value are omitted. 


1. KNOB CONE x MONTEREY (P. attenuata Lamm, x radiata D. Don). 1927. 

Described as x P. atterjuradiata Stockwell and Righter (9). 
Occurs spontaneously in Santa Cruz County, California. The cross 
made at IFG utilized the economic ally -unimportant Sierra foothill 
race of knobcone pine, which is more cold-resistant but less vigor- 
ous than Monterey pine and the coastal forms of knobcone pine . 
Hybrid is intermediate between the parents in growth-rate, cold- 
resistance, stem-form, and flowering-time (9) . 

Should be tested up to 3*000 feet on the west slope of the 
Sierra Nevada against ponderosa pine, and its more promising 
hybrids and against other commercially important species of forest 
trees. At IFG the Monterey-knob cone hybrid appears to outgrow 
ponderosa pine by at least 10 percent in height and diameter up 
to 23 years (present age of oldest hybrids). Should also be 
tested up to 3>000 feet in the Coast Ranges on ponderosa pine and 
Douglas fir sites. Should be of value on colder margins of areas 
where Monterey pine is grown successfully (e.g. Australia, New 
Zealand, South Africa, Spain, Portugal, Chile, Argentine). 

Wood tested at Forest Products ^Laboratory (i) was roughly 
comparable to that of ponderosa pine in density and longitudinal 
shrinkage . 

2. KNOBCONE x BISHOP (P. attenuata x muricata D. Don). 1946. 

In early tests at IFG appears to outgrow both parents. Stem 
form unknown. No recommendations for use can be made at present. 

3. SHORE (closely related to lodgepole pine) x JACK (P.. ccntorta 
Dougl . x banksiana Lamb . ) . ~ 194-6 . 

In early tests at IFG outgrows shore pine and equals jack 
pine. Depending on development of market for shore pine as source 
of pulpwood, this may be of value in coastal Oregon, Washington, 
and British Columbia; possibly also in British Isles, coastal 
Norway, and Belgium. Stem form unknown. 

4. LODGEPOLE x JACK (P. contorta var. latifolia Engelm. x banksiana ) . 

Occurs spontaneously in Alberta (5.) . Described as x P. 
mur r ayb ank s i ana Righter and Stockwell (6). In tests at IFG, 
central Wisconsin, northern Idaho, and eastern Massachusetts, out- 
grows California lodgepole in height and diameter. Early growth 
about equal to that of jack pine, but in several localities, after 
several years, the jack pine falls behind the hybrid. Produces 
cones in third or fourth year. Should be valuable for pulpwood 


production. Should be tested in Pacific Northwest, northern Rocky 
Mountains, Lake States, northern New York, New England, and Ontario, 
Quebec, and Maritime Provinces of Canada. Likewise in British 
Isles, northern Europe, northeast Asia, and those parts of Australia 
and New Zealand where lodgepole pine has been successful. 

5. SANTA CRUZ ISLAND x MONTEREY (P. remorata Mason x radiata ) . 1942. 

Grows at about the same rate as both parent species. Has 
good form. This hybrid should be tested as a potential replacement 
or alternative type wherever Monterey pine is used. Tests should 
include resistance to insects such as Sirex noctilio , spider mites, 
and other pests which, in certain localities, Impair the productivity 
of Monterey pine. 

6. JEFFREY x COULTER (P. jeffreyi Grev. & Balf. x coulter i D. Don). 
1944 • 

Occurs spontaneously wherever parent species occur together. 
In tests at IFG outgrows Jeffrey pine and is somewhat slower growing 
than Coulter pine. So far, this cross has yielded very low propor- 
tions of sound seeds. Therefore, the backcross hybrid listed below 
is considered of greater practical importance. 

7. JEFFREY x (JEFFREY-COULTER) (P. .jeffreyi x ( jeffreyi x coulteri ) ) . 

Pollen from a natural hybrid (10) . Yields of seed of this 
backcross are very high. Cage-tests at IFG suggest that this hybrid 
is more resistant than Jeffrey pine to the pine reproduction weevil 
which has caused high mortality in plantations of Jeffrey and ponderosa 
pinefe in northern California. Preliminary results of uncaged tests 
in 'localities in northern California, where the insect abounds, give 
weight to the suggestion. The hybrids grow at approximately the same 
rate as ponderosa pine, and have equally good stem form and branching 
habits. In view of the susceptibility of ponderosa pine to the pine 
reproduction weevil, these circumstances combine to make this back- 
cress the most promising hybrid yet produced for use in the California 
region. It is therefore being tested, under field conditions, through- 
out the California pine region. It may not offer any advantage, however, 
in comparison with ponderosa pine in regions not infested with the pine 
reproduction weevil. 

8. PONDEROSA x APACHE (P. ponderosa x latifolia Sarg.).' 1943. 

This hybrid outgrows both parent species, and is of great promise 
for use in the California pine region, and perhaps in southwestern 
U.S. and northern Mexico. It is susceptible to attacks of the pine 
reproduction weevil but, due to its greater vigor, it outgrows suscep- 
tibility to the insect more quickly than does ponderosa pine. 
Nevertheless, steps are being taken to introduce reproduction weevil 
resistance from Coulter pine. 


9. PONDEROSA x ARIZONA (P. ponderosa x ponderosa var. arizonica 
(Engelm.) Shaw). 1946. 

This hybrid slightly outgrows ponderosa in height. Its early 
performance in plantations at 6,000 feet on the Stanislaus National 
Forest in California is excellent. It should be tested throughout 
the California pine region, in southwestern U.S., and in northern 
Mexico . 

10. PONDEROSA x MONTEZUMAE (P. ponderosa x montezumae Lamb.). 1946. 

In nursery tests at Placerville, this hybrid outgrows ponderosa 
in height. It should be tested throughout the California pine region, 
in southwestern U.S., and in northern Mexico. 

var. scopulorum Engelm. ) . 1941. 

The hybrid outgrows the Rocky Mountain variety and equals the 
coastal and Sierra Nevada forms in tests at IFG. It may, therefore, 
merit trial in the Rocky Mountain and Black Hills regions where its 
cold -hardiness must be tested. 

12. SHORTLEAF x SLASH (P. echinata Mill, x caribaea More let). 1931. 

In tests at IFG appears to have narrower crown and finer 
branches than shortleaf . Potential value seems to be in putting a 
faster growing, better formed tree on shortleaf pine sites to the 
north and west of natural distribution of slash pine. May prove to 
have some value in developing a pine more resistant to fusiform 
rusts than slash pine, in which case it may be of importance in the 
general range of slash pine. Should be tested in areas to north 
and west of natural distribution of slash pine. 

13. SHORTLEAF x LOBLOLLY (P. echinata x taeda L. ) . 1933. 

According to unpublished observations, occurs spontaneously 
in east Texas and perhaps elsewhere. In tests at IFG outgrows 
shortleaf in height and diameter by about 10 percent, and has shown 
great resistance to cold in southern Illinois. May be of value on 
shortleaf sites. Should be tested throughout natural distribution 
of shortleaf pine. 

14. PITCH x LOBLOLLY (P. rigida Mill, x taeda ). 1933- 

This hybrid grows faster and has better form than pitch pine 
but in tests in Maryland has seemed inferior to loblolly. It has 
outgrown loblolly pine in New Jersey, and shortleaf pine in southern 
Illinois where it appears to be more frost resistant than both lob- 
lolly and shortleaf pine. It should be tested north of the distri- 
bution range of loblolly pine in pitch pine areas, and in Illinois 
where it may produce a tree of better form and faster growth than 
pitch pine . 


15. LOBLOLLY x SLASH (P. taeda x caribaea ) . 1931. 

In small test at IFG, this hybrid appears to have somewhat 
better form than loblolly. May be valuable in bringing a better- 
formed, faster-growing tree into the loblolly region, and in 
breeding a slash pine more resistant to fusiform rust. Should be 
tested throughout the loblolly pine region. 

16. SUGAR x ARMAND'S (P. lambertiana x armandi Branch. ). 1947. 

Yields of seed following this cross are very low. Never- 
theless, as Armand's pine is highly resistant to blister rust, this 
hybrid may be of value in developing blister-rust-resistant sugar 
pine. The first tests will be inoculation or exposure tests to 
determine the degree of blister-rust resistance of this hybrid. 

17. SUGAR x KOREAN (P. lambertiana x koraiensis Sieb . & Zucc). 1947. 

This cross, likewise, is difficult to make; so far only one 
seedling has been produced. As Korean pine is highly resistant to 
blister rust, this hybrid should also be of value in developing 
blister-rust-resistant sugar pine, and promises to be more cold 
resistant than the sugar x Armand's hybrid. 

18. WESTERN WHITE x EASTERN WHITE (P. monticola Dougl. x strobus L.). 

This hybrid is of special interest because it has outgrown 
both parent species In numerous tests made at IEG. Several geo- 
graphic races of both parent species have been used in this cross, 
always resulting in vigorous hybrids. Therefore, this hybrid should 
be tested throughout the distribution ranges of both parent species. 
The finding in both species of individuals which are apparently 
resistant to blister rust (2_]_, (8), Inspires hope that vigorous 
resistant hybrids will soon be produced. 

19. WESTERN WHITE x HIMALAYAN WHITE (P. monticola x griffithi McClell.). 

This hybrid outgrows western white pine and appears to be less 
susceptible to blister rust than that species. The hybrid grows at 
about the same rate as Himalayan white pine, but Is more drought 
resistant. The hybrid should be tested throughout the distribution 
range of western and eastern white pines, but may not be completely 
cold hardy in the colder parts of these regions. 



WESTERN WHITE x BALKAN WHITE (P. monticola x peuce Griseb.). 1947. 

This hybrid grows no faster than western white pine but may 
combine cold hardiness and moderate resistance to blister rust. Tests 
of its susceptibility to blister rust must precede tests of its growth 
in the field. 

21. WESTERN WHITE x (BALKAN WHITE x EASTERN WHITE) (P. monticola x (peuce 
x strobus ) ) . 1946. 

This hybrid grows at about the same rate as the vigorous western 
white x eastern white hybrid. Its value will depend on the outcome of 
blister-rust-resistance tests. 

22. LIMBER x HIMALAYAN WHITE (P. flexilis James x griffithi ) . 1947. 

In early test at IFG outgrows limber pine by 100 percent in 
height. Should be of value as a blister-rust-resistant ornamental 
white pine with greater cold resistance than Himalayan white pine. 
Should be tested for both rust and cold resistance. Value as a timber 
tree cannot yet be estimated, but its rate of growth is extremely 
rapid for white pine . 

23. EASTERN WHITE x HIMALAYAN WHITE (P. strobus x griffithi ). 1940. 

This hybrid has shown good resistance to blister rust in a 
rigorous exposure test in Oregon. It outgrows eastern white pine 
and is about equal to Himalayan white and should be tested in the 
distribution ranges of eastern and western white pines as well as 
in those parts of Europe where the good growth of eastern white 
pine is offset by its blister rust susceptibility. 



Anderson, E. A. 1949. Specific gravity and shrinkage of Pinus 
attenuata x radiata . Forest Products laboratory, Madison 
Wisconsin. 7 p., 7 tables, 2 figs. (Typewritten report) 

Bingham, R. T., A. E. Squillace, and J. W. Duffield. 1953. 
Breeding blister-rust-resistant western white pine . 
Jour. Forestry 51: 163-168. 

Kelsey, H. P. and W. A. Dayton. 1942. Standardized plant names 
Mc Far land, Harrisburg. 675 p. 

Miller, J. M. 1950. Resistance of pine hybrids to the pine 

reproduction weevil. California Forest and Range Exper- 
iment Station. Research Note No. 68. 17 p. 

Moss, E. H. 1949. Natural pine hybrids in Alberta, Canada. 
Jour. Research, C. 27: 218-229. 

Righter, F. I., and P. Stockwell. 1949. The fertile species 
hybrid, Pinus murraybanksiana . Madrono 10: 65-69. 

Righter, F. I. and J. W. Duffield. 1951. Interspecies hybrids 
in pines. Jour. Heredity 42: 75-80. 

Riker, A. J., T. F. Kouba, W. M. Brener, and L. E. Byam. 1943. 

White pine selections tested for resistance to blister 
rust. Jour. Forestry 41: 753-760. 

Stockwell, W. P. and F. I. Righter. 1946. Pinus: the fertile 
species hybrid between knobcone and Monterey pines. 
Madrono 8: 157-160. 

Zobel, B. J. 1951. The natural hybrid between Coulter and 
Jeffrey pines. Evolution 5: 405-413.